Wear resistant belts, and a process for their manufacture

ABSTRACT

Endless power transmission belts and processes for their manufacture, having power transmitting surfaces comprising a wear resistant composite, which belts exhibit improved abrasion- or wear resistance, reduced noise, reduced frictional heat generation, and improved dimensional stability compared to known belt constructions, as well as processes for manufacturing same. More particularly, an endless toothed belt having an abrasion- and noise resistant cover element, which comprises at least one friction-modifying constituent and at least one binder constituent.

BACKGROUND OF THE INVENTION

The present invention relates to endless belts having power transmittingsurfaces exhibiting high wear resistance, and more particularly toendless toothed belts having a wear-resistant fabric cover intimatelypositioned along the outer surface of the tooth and land portions of thebelt, and having a coating adhered to the outer surface of andpreferably partially penetrated into the fabric cover, as well as to amethod for producing such belts. The coating comprises a wear-resistantcomposite, which provides improved wear- or abrasion resistance andimproved frictional characteristics to the belt, particularly under highload operation thereof.

Endless belts, including V-belts, V-ribbed belts, and flat belting, aswell as toothed belts such as synchronous or timing belts and the like,are used in a variety of applications. Examples of power transmissionbelts, including toothed or synchronous belts, V-belts, and V-ribbedbelts are disclosed in U.S. Pat. Nos. 3,138,962; 3,200,180; 4,330,287;and 4,332,576. Examples of methods for producing such belts aredisclosed in U.S. Pat. No.3,200,180 as indicated above and U.S. Pat.Nos. 3,772,929 and 4,066,732. These patent references are merelyexamples of various types of power transmission belts andstate-of-the-art formation techniques thereof.

Toothed belts, generally comprising an elastomeric body portion, anessentially non-extensible reinforcing member and a plurality of drivingteeth extending along the underside of the belt at a predeterminedpitch, are put to particularly good use in high temperature, high speedand/or high load environments, including various industrial andautomotive drive systems. In automotive applications, there is a growingdemand for toothed belts which can perform successfully underincreasingly high loads and at average operating temperatures of about120° C. Operating temperature requirements for such applications areexpected to reach 150° C. or greater in the near future.

Under such high load, high temperature and/or high-speed conditions, itis common for the teeth of endless toothed belts to deteriorate; thesevere shearing stresses on the teeth often result in crack generationand tooth loss. A wear-resistant fabric cover element is used over thetooth and land portions of such belts to shield the elastomeric teethfrom such stresses. This modification alone however has not provedcompletely satisfactory in some particularly demanding applications.Upon extended high load or high-speed operation, such fabric covers tendto wear away, resulting in dimensional changes and/or premature beltfailure. Moreover, there is a tendency in such constructions for theunderlying belt elastomer to migrate through the weave of the fabriccover during the curing process and/or upon operation, and to thusbecome exposed at the belt's power transmitting surface. The presence ofthis relatively high coefficient of friction material at the belt'spower transmitting surface results in high noise and frictional heatgeneration at the belt-sprocket interface upon operation of the belt.Noise generation is viewed as highly undesirable, and frictional heatgeneration and heat build-up reduce the life of the belt.

One proposed solution to the noise generation and/or frictional heatbuild up problems common in conventional belt operation has been toreduce the effective coefficient of friction of the power-transmittingsurface of the belt. One such approach involves isolating or removing asmuch of the elastomer as possible from near the surface of the beltwhere that surface comes in contact with sprocket teeth. Such anapproach is taken for example in U.S. Pat. No. 3,772,929, wherein theouter surface of a wear-resistant fabric covering is kept free of beltelastomer, by the presence of a bonded layer of elastomer imperviousmaterial adhered to such outer surface.

A second approach has been to incorporate a relatively purepolytetrafluoroethylene (PTFE) layer over the wear-resistant fabriccover element to decrease the effective coefficient of friction of thedriving surface of the belt.

A third approach, directed moreover to improving abrasion resistance,has involved coating the motion-transmitting surfaces of a belt with apolymer matrix comprising a fluorine-containing plastic. In EuropeanPatent Publication No. 0662571 A1, a process for producing the belts isdisclosed including the steps of applying such matrix onto themotion-transmitting surfaces of the belt, and then drying the matrixsuch that it goes through a crosslinking process for bonding itself tothe elastomeric belt element.

None of these approaches to the problems of abrasion, noise and/orfrictional heat generation in endless belt constructions is believed tobe completely satisfactory, particularly in very high load applications.Where the belt surface remains free of belt elastomer by means of arelatively poor abrasion-resistant or low temperature laminate coatingon the outer surface of a fabric cover element, high load or hightemperature operation generally results in flaking off or melting of thecoating. Generally, as a low temperature, low abrasion-resistantlaminate flakes or melts off of the fabric layer with continued use, thedistance between the center of the load carrying members of the belt andthe bottom surface of the land portions between adjacent longitudinallyspaced teeth decreases. This dimensional change affects the pitch linediameter of the belt and results in poor tooth-sprocket fit, henceincreased belt noise. Moreover, as the coating layer diminishes, thefabric cover becomes exposed to the sprocket, ultimately leading todeterioration of such layer and exposure of the belt elastomer.

A substantially pure PTFE layer incorporated on the surface of awear-resistant fabric cover element, while producing a reducedcoefficient of friction at the driving surface, exhibits very poor wearresistance, and thus would likely wear off of the belt with use, againleaving the wear-resistant fabric layer exposed and presenting theconcomitant problems associated therewith, described above.

The incorporation of a coating on a wear-resistant cover element, whichcomprises a matrix cross-linkable with the belt body and containing afluorine-containing plastics material, is believed to be similarlyinadequate. Application of such coating onto a fabric surface accordingto the teachings of that disclosure has been found to result indeposition of only a relatively thin layer at the belt surface, whichhas been found to exhibit inferior wear resistance. It is believed thatin the construction proposed in the reference, a relatively large amountof the total fabric cover thickness remains free of the coatingmaterial, hence fiber-to-fiber abrasion occurs within the fabric uponoperation of the belt. This is believed to lead to a wearing away ofportions of the fabric itself, and thus potentially diminished operatinglife.

Thus, known endless belt constructions or processes for theirmanufacture have not effectively addressed the combined problems of beltnoise, frictional heat generation, and dimensional instability.

Consequently, there remains a need to produce an endless belt, includingan endless toothed belt for use in high temperature dynamicapplications, which exhibits improved wear resistance, reduced noiseduring belt operation, which does not exhibit significant frictionalheat generation, and which otherwise remains dimensionally stable for anappreciable, predictable operating lifetime.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the invention to provide anendless belt which overcomes drawbacks of prior constructions, and inwhich the belt exhibits reduced noise generation, reduced heatgeneration, improved wear resistance and dimensional stability, all overa generous, predictable operating lifetime.

It is another object of the present invention to provide a method forproducing belts of the aforementioned type.

It is a further object to provide such belt which exhibits exceptionaladhesion between the fabric cover and wear-resistant coating on the onehand, and the underlying elastomer belt elements on the othersubstantially throughout its operating life.

To achieve the foregoing and other objects and in accordance with apurpose of the present invention as embodied and broadly describedherein, a power transmission belt is provided, having an elastomericbody portion and a fabric cover element covering at least thewear-dependent, power transmitting portions of the belt, and having awear-resistant, friction-modifying composite coated on the surface ofthe fabric cover element, and penetrated into within at least a portionof the total thickness of the fabric cover element, preferably such thatthe wear-resistant composite is substantially separated from theelastomeric body portion by a boundary. In a preferred embodiment, atleast a portion of the friction-modifying constituent of thewear-resistant composite is separated from the matrix portion of thewear-resistant composite, by a gap or boundary.

In a further embodiment, a method for the manufacture of an endless beltof the type noted above is provided, comprising the steps of treating afabric cover element with a fabric treatment material comprising atleast one cross-linkable constituent, such that at least one of thevoids in the fabric remains at least partially free of the fabrictreatment material; applying a wear-resistant, friction-modifyingcomposite comprising at least one binder constituent and onefriction-modifying constituent to a first surface of the fabric coverelement; causing at least a portion of the wear-resistant composite topenetrate at least a portion of the total thickness of the fabric coverelement so that some of the friction-modifying constituent resideswithin one or more voids in the fabric; and polymerizing thewear-resistant composite. Belts which may be beneficially producedaccording to the claimed method include V-belts, V-ribbed belts, flatbelting or toothed belts such as synchronous or timing belts,

In still another embodiment, an endless belt is provided wherein awear-resistant, friction-modifying composite coats the outer surface ofand penetrates into a portion of the total thickness of the fabric coverelement, but does not penetrate through the entire thickness thereof.

In yet another embodiment, an endless toothed belt and a process for itsmanufacture are provided, the belt having a tensile-loaded body portioncomposed of an elastomeric material, a plurality of spaced teeth bondedwith and disposed along at least the inner periphery of the bodyportion, a layer of wear-resistant fabric positioned substantially alongthe periphery of at least the alternating teeth and land portions of thebelt, and a wear resistant, friction modifying composite layerpositioned substantially along the outer surface of, and penetrated intoat least a portion of, the wear-resistant fabric. The process ischaracterized in that the fabric cover element is first treated with afabric treatment material containing at least one cross-linkableconstituent, at a pick-up rate of from about 1% to less than about 30%,based on fabric weight; the wear-resistant composite is applied to afirst, power transmitting surface of the fabric cover, thecomposite-coated fabric cover element is applied to the belt bodyportion, and the belt is cured or vulcanized. In this embodiment, theendless belt may be of any conventional form wherein a wear-resistantfabric is positioned along at least the tooth and land portions of thebelt, including for example, synchronous or timing belts and dual-sidedtoothed belts.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing which is incorporated in and forms a part ofthe specification, illustrates a preferred embodiment of the invention,and together with the description, serves to explain the principles ofthe invention. In the drawing:

FIG. 1 is a fragmentary, perspective view of a synchronous beltconstructed in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, an endless synchronous-type power transmission belt10 is shown generally. The belt includes a body having an overcordsection 12 formed from a suitable elastomeric material and a series ofspaced cogs or teeth 16, also comprising a suitable elastomeric material14. The elastomeric material or materials utilized in the overcordsection 12 and teeth 16 should be compatible with one another and may beof the same or of different types of elastomer. Any suitable castable ornon-castable elastomer may be used as the overcord or belt bodyelastomer, and/or the tooth portions in this embodiment of the presentinvention, but in a preferred embodiment at least one and preferablyboth of the overcord portion 12 and the teeth 16 of the belt 10 areformed of a suitable hydrogenated acrylonitrile butadiene rubber (HNBR)composition.

The elastomer overcord section 12 is preferably loaded with areinforcing tensile layer or a plurality of tensile members, many ofwhich are well known to the art, such as the longitudinally extendingand spaced tensile cords 18 as shown. These tensile members may consistof one or more strands of any suitable stress-resistant materialincluding but not limited to polyamide cord, aramid cord, glass fibercord, carbon cord, polyester cord or filament wire cord, typicallydisposed as one or more embedded helically-wound cords. The tensilemembers may be pre-stressed or impregnated with a suitable material aswell known in the art, if desired. The elastomeric belt body maypreferably be loaded with discontinuous fibers as is well known in theart, by the incorporation within the elastomer of suitable and/orconventional material including staple fiber, pulp fiber of choppedfiber reinforcement materials. Suitable materials for fiber loadinginclude for example aramids, including meta- and para-aramids, such asthose available by DuPont Chemical Co. under the trademark, KEVLAR;nylon, polyester and cotton. Fiber loading may be at any level suitablefor the application, and may include orientation of at least asubstantial number of the fibers in a direction perpendicular to thetravel of the belt. One or more such fibers may moreover protrude fromthe elastomeric material as is generally known.

A wear-resistant fabric layer 22, or reinforcing fabric cover elementintimately fits along at least the alternating teeth 16 and alternatingland portions 24 of the belt 10 as shown to form a face cover therefor.This fabric may be of any desired configuration such as a conventionalweave consisting of warp and weft threads at any desired angle, or mayconsist of pick cords, or of a knitted or braided configuration, or thelike. More than one ply of fabric may be employed. If desired, thefabric may be cut on a bias so that the strands form an angle with thedirection of travel of the belt. Conventional fabrics may be employedusing such materials as cotton, polyester, polyamide, aromaticpolyamide, hemp, jute, fiberglass and various other natural andsynthetic fibers. In a preferred embodiment of the invention, the fabriclayer 22 comprises an expansible wear-resistant 3×3-twill weave fabricin which at least one of the warp or weft threads is formed of nylon6,6. At least one of the warp or weft yarns may moreover be texturized,twisted and/or otherwise processed, as is well known in the art.

In a more preferred embodiment of the present invention to be describedin further detail below, the fabric comprises nylon 6,6 yarns having atensile strength of at least 6.0 g/decitex in their initial state inboth the warp and weft directions. At least one of the warp and weftyarns is preferably texturized, or woolly processed, to yield a fabrichaving at least 80% elongation at a 2-kg load, as measured on a 25 mmstrip. According to this same preferred embodiment, the finished weightof the fabric is preferably at least 385 g/m², of which at least 90% ofthe weight is preferably in the woolly processed direction, i.e., in thedirection of travel of the belt.

A wear-resistant, friction-modifying composite 20 is positioned along atleast a portion of the outer surface of the fabric cover element 22. Thecomposite 20 is applied and/or fabric cover 22 treated so that, in apreferred embodiment, the coating penetrates at least a substantialportion of the total thickness of the wear-resistant fabric layer 22. Ina more preferred embodiment of the invention, the wear-resistant,friction-modifying composite 20 penetrates less than the entirethickness of the fabric layer 22.

In an additional preferred embodiment, a second fabric cover element(not shown) may be utilized on the outer surface of the overcord section12 of the power transmission belt 10 opposite that having tooth 16 andland 24 portions. This second fabric cover element may be of the same ordifferent materials and construction as those set forth above, and maypreferably furthermore include a wear-resistant composite as describedabove and in further detail below, or any other type of suitablecoating. As is generally known in the art, the incorporation of suchadditional fabric cover element on a surface of the belt remote from thepower transmitting surface has been found to increase the overall wearresistance of the belt, thus potentially improving the operating lifeexpectancy thereof.

The novel use of a wear resistant composite layer according to oneembodiment of the present invention, as a coating upon and penetrantwithin a wear-resistant fabric tooth and land covering of an endlesstoothed belt overcomes the shortcomings of the prior art, by providing afinished endless toothed belt which exhibits minimal noise, whichretains substantial dimensional stability for the life of the belt,which exhibits improved wear- or abrasion-resistance properties andwhich minimizes frictional heat generation during operation of the belt.The novel use of such wear-resistant, friction modifying composite whichpenetrates a substantial portion, but less than the entire thickness ofa fabric cover overcomes shortcomings of the prior art by providing anendless toothed belt which exhibits improved adhesion between the fabriclayer and wear-resistant composite on one side, and the belt elastomeron the other. According to the present invention, the wear-resistant,low coefficient-of-friction coating is believed to penetrate at least aportion of the fiber bundles and interstices between individual yarns,to reduce fiber-to-fiber abrasion within the fabric, thus reducing thispotential source of fabric wear. The present construction is believed tomoreover form an appreciable reservoir of friction-reducing materialinside the fabric cover element, and essentially continuously lubricatethe fibers at the tooth-sprocket interface for essentially the entire,undiminished operating lifetime of the belt.

The wear resistant, friction-modifying composite useful in the practiceof the present invention preferably exhibits sufficient flexibility tobe utilized successfully in belts which may be driven about theincreasingly small radius sprockets and/or sheaves commonly encounteredin automotive engine compartments. The composite preferably comprises africtional modifier, which imparts a reduced coefficient of friction tothe composite, and a resin, or other suitable binder, which contributesto the abrasion-resistance properties of the material. To facilitateapplication of the composite in the belt-building process, the compositemay preferably be contained in a carrier solution, e.g., water or anorganic solvent, which may preferably be allowed to liberate uponapplication of the composite to the associated workpiece.

In a preferred embodiment, the wear resistant composite useful in thepresent invention comprises a dispersion of one or morefriction-modifying components in the form of fluoropolymers in a carrieror binder. In a preferred embodiment, the fluoropolymers include but arenot limited to polytetrafluoroethylene polymers (PTFE),polytrifluoromonochloroethylene polymers (PTFCE), polyvinylidenefluoride polymers (PVDF), fluorinated ethylene polymers (FEP) andperfluoroalkoxy polymers (PFA). Additional friction-modifying materialswhich may be beneficially employed in the regard for example may includemolybdenum disulphide and graphite.

The wear-resistant composite moreover preferably comprises one or morebinder resins for facilitating the coating process and for contributingto the performance of the final coating. The resin or resins may be anysuitable material or blend thereof within which the frictional modifiermay be dispersed or suspended, and which may or may not be polymerizableas by cross-linking or chain-extension, with itself and/or theunderlying belt materials, but which is preferably at least partiallypolymerizable, i.e., cross-linkable or capable of chain extension, toimprove bonding of the coating within the belt construction. In apreferred embodiment, the composite binder forms a matrix within whichthe friction-modifying constituent is dispersed in the final coating.According to this preferred embodiment, at least a portion of thefriction-modifying constituent, which may be in the form of individualparticles or groups of such particles dispersed throughout the matrix,is at least partially separated from the binder constituent by gaps orboundaries. While not intending to be limited to a particular theory, itis presently believed that this separation of at least a portion of thefriction-modifying constituent from the material of the binder matrixwithin which it is dispersed provides a beneficial effect in the finalbelt, without adversely affecting adhesion between the frictionalmodifier and binder constituents, or between the wear-resistantcomposite and the fabric cover element. It is presently believed thatthe gaps or boundaries between portions of frictional modifier particlesand the surrounding binder matrix allow for some degree of movement ofthe particles within the matrix. This attribute is furthermore believedto contribute to the continuous lubrication of individual fabric coverelement fibers to decrease wear thereof, and to provide an essentiallycontinuous source of additional frictional modifier material at thebelt-sprocket or -sheave interface.

This highly wear resistant composite remains substantially intact on thebelt's surface for the useful life of the belt, and preferably generallywill not melt off at the high temperatures now commonly encountered inengine compartments. The wear resistant composite has good abrasion- orwear resistance, and therefore does not readily flake or wear off of thewear-resistant fabric cover element of the endless belt during thebelt's life. The composition exhibits an effective coefficient offriction which is preferably lower than the coefficient of friction ofthe belt body elastomer thus reducing overall frictional heat build-upand noise-generation characteristics, and improving the overallefficiency of the belt. Preferred composites for use in the practice ofthe present invention are generally commercially available, and maypreferably comprise a blend of binder resins, pigments and fluoropolymerresins, in industrial organic solvents. The coating material preferablyexhibits flexibility up to or exceeding 100% extension. Materials mostpreferred at present as the wear-resistant composite in the practice ofthe present invention are available from Whitford Plastics Limited,under the trademark, XYLAN, and comprise blends of binder resins,pigments and fluoropolymer resins in one or more industrial organicsolvents.

The wear-resistant composite of the present invention is distinguishablefrom the incorporation of a substantially pure PTFE layer over thefabric layer of endless toothed belts. As noted above, a substantiallypure PTFE layer exhibits relatively poor wear resistance and thereforewould likely wear off of the belt surface with use. While not intendingto be limited to one particular theory, it is presently believed that inthe subject invention, wherein a fluorinated polymer such as PTFE isconversely used as a frictional modifier within a highlyabrasion-resistant composite matrix, the PTFE does not wear off with usebut remains on the driving- or power transmitting surface of the beltfor its intended operating lifetime.

It is contemplated that the improvement provided by the presentinvention would provide significant benefits in all endless beltapplications. In such applications, the wear resistant composite forms acoating upon, and a penetrant within at least a portion of the totalthickness of a fabric cover element. Both castable and non-castableelastomers may be used as the elastomeric belt portions in thisembodiment of the present invention. Examples of suitable castableelastomers include but are not limited to castable polyurethanes(including polyurethanes, polyurethane/ureas and polyureas), plastisols,organosols, liquid chloroprenes, liquid polysulfides, liquid rubbers,silicones, epoxides, urethanes, polyester based resins, polyether basedresins, and the like, as well as blends or mixtures thereof.Polyurethane elastomers are generally preferred over other types ofcastable elastomers at present because of their favorable tensilestrength and abrasion resistance and their satisfactory modulus andelasticity. These polyurethanes may be prepared in any conventionalmanner, such as by compounding a polyurethane prepolymer with a chainextending agent, and optionally an amount of plasticizer or otheringredient if desired. Conventional chain extenders may be utilized,which are generally known to the art.

Non-castable elastomers useful as the belt body portions of such beltswhich would likely enjoy the benefits provided by the present inventioninclude for example, chloroprene rubber (CR), acrylonitrile butadienerubber (NBR), hydrogenated NBR (HNBR), styrene-butadiene rubber (SBR),alkylated chlorosulfonated polyethylene (ACSM), epichlorohydrin,butadiene rubber (BR), natural rubber (NR) and ethylene propylene dieneterpolymer elastomer (EPDM), as well as blends or mixtures thereof. Mostthermoplastic elastomers are also envisioned within this context.Whether a castable or non-castable elastomer is utilized in thecompositions, which form the elastomeric portion(s) of the belt, suchcompositions may also generally include conventional additives inamounts generally suitable for use in the intended application. Thus forexample, such composition may also include a reinforcing, partiallyreinforcing or non-reinforcing filler in amounts of from about 0 partsper hundred weight of rubber (phr) to about 500 phr; one or moreplasticizers in amounts of from about 0 phr to about 30 phr; one or morevulcanization agents or curatives, including sulfur,free-radical-generating materials such as peroxide and ionizingradiation, etc., in amounts of from about 0 phr to about 30 phr; one ormore co-agents or activators in amounts of from about 0 to about 100phr; and one or more antidegradants in amounts of from about 0 phr toabout 15 phr etc. In a preferred embodiment of the present invention, atleast one of the elastomer overcord portion and elastomer tooth portionis formed of a suitable HNBR elastomer composition.

The present invention contemplates a process for the production of thebelts described above. It is characterized in that a fabric coverelement is first treated, preferably by immersion in a suitablecross-linkable material compatible with the elastomeric portions of thebelt, optionally in combination with a resin such as resorcinolformaldehyde. This first treatment is performed in such a way that atleast a portion of the voids or interstitial spaces formed between theindividual fibers and yarns of the fabric cover element remain at leastpartially free of the treatment material. This allows a significantamount of the wear-resistant composite, applied in a subsequent step, topenetrate at least a portion of the total thickness of the fabric, andto enter into and remain within such voids and interstitial spaces. Thepick-up rate of such fabric treatment material is preferably from about1% to about 50%, more preferably from about 5% to less than about 30%,even more preferably from about 7% to about 25%, and is most preferablyfrom about 10% to about 20%, based on the particular fabric weightemployed. While this is a relatively low pick-up rate, it has beensurprisingly found that its effect in permitting the wear-resistantcomposite through at least a portion of the fabric and to permeate theinterstices between at least a significant portion of the yarns of thefabric is quite dramatic.

It is not uncommon for fabrics intended for use as belt cover elementsto be rubberized by treatment with a suitable cross-linkable-containingmaterial. Typical pick-up rates for treating fabric cover elements inorder to rubberize them however is generally from about 30% to about 40%or more. Conversely, according to the present invention, it has beenfound that deposition of the fabric treatment material in the claimedamounts sufficiently coats the fibers and yarns of the fabric coverelement, while leaving sufficient voids in the fabric within which thewear-resistant composite may penetrate and take hold. Increasing theamount of fabric treatment material in this treatment step has beenfound to reduce the amount of wear-resistant, frictional-modifyingcoating, which can penetrate the fiber cover element. Thus, while arelatively low amount of fabric cover treatment material serves to allowthe coating to penetrate at least a portion of the fabric's totalthickness, it has been found that increasing the amount of thistreatment actually has a negative impact on the final belt'sperformance. The improvement in wear resistance provided by the presentinvention, as evidenced in the comparative test results set forth below,is dramatic.

As a second step, the wear-resistant, friction-modifying composite isapplied to at least, but preferably only one side of the thus treated orpartially rubberized fabric. Application of the composite may be by anysuitable method, including spraying, knife-coating etc., but ispreferably by knife-coating, at a pick up rate of preferably from about5% to about 80%, more preferably from about 20% to about 50%, and mostpreferably from about 25% to about 35%, based on the dry fabric weight.

As an optional but preferred third step, a second application of atleast one cross-linkable material, preferably in a resin-type carriersuch as in a resorcinol formaldehyde latex, is effected on a second sideof the fabric, i.e., to the surface of the fabric opposite that of thewear-resistant coating. This application is believed to contributeadditional adhesive strength to the bond between the fabric layer andthe underlying belt elastomer, and to contribute to the formation of abarrier or boundary between the fabric cover and wear-resistant coatingon one hand, and the underlying elastomeric belt members on the other.This material may be the same as or different from the fabric treatmentmaterial noted above, but is preferably compatible with the balance ofthe belt components. Application of this material may be by any suitablemethod including spraying and knife-coating, but is preferably byknife-coating at a pick-up rate of from about 2.5% to about 55%, morepreferably from about 15% to about 50%, and is most preferably fromabout 20% to about 35%, based on the dry fabric weight.

An adhesive treatment may then optionally but preferably be applied tothe same second side of the fabric, i.e., the surface of the fabricopposite that of the wear-resistant composite. This adhesive treatmentmay preferably be in the form of any suitable and/or conventional rubberadhesive composition appropriate for use with the balance of the beltcomponents, many of which are well known in the belt-building art,including but not limited to those available from Compound IngredientsLtd., under the trademark, CILBOND 80, and similar adhesives availablefrom The Lord Corporation. Application of this adhesive treatment may beby any suitable method including spraying and knife-coating, but ispreferably by knife-coating at a pick-up rate of from about 0 to about70%, more preferably of from about 1% to about 40%, and most preferablyof from about 10% to about 25%, based on the dry fabric weight.

As an additional optional but preferable step, an additional adhesivetreatment may be applied to the second side of the treated fabric. Anysuitable and/or conventional adhesive material compatible with thesurrounding belt materials may be employed in this regard, in amountstypically employed for the purpose. In a preferred embodiment, at leastone cross-linkable material compatible with the belt body elastomer isemployed in this regard, preferably suspended or dispersed in a suitablesolvent which may be liberated upon application of the adhesivecomposition. Application of such second adhesive treatment material,intended to contribute to the adhesive bond between the fabric layer andthe belt body elastomer, may be by any conventional method includingspraying, knife coating, etc. The pick-up rate of this material in thefabric cover element may be from about 3% to about 110%, preferably fromabout 25%. to about 80%, and is most preferably from about 40% to about70% based on the dry fabric weight.

As one skilled in the relevant art would readily appreciate, the fabricshould preferably be allowed to dry between each of the successivetreatment material applications noted above. Particularly with regard tothe application of the wear-resistant, friction-modifying composite tothe fabric cover element surface, where, as in a preferred embodiment,the binder constituent is capable of curing, cross-linking orchain-extension, or otherwise polymerizing, the drying operation shouldinvolve sufficient time, temperature, and/or other condition to allowfor same.

As is well known in the art, fluoropolymers including PTFE exhibitvirtually no adhesion to most substrates. Thus, in the present instanceit is highly desirable for the wear-resistant composite matrixcontaining such fluoropolymers to remain remote from the beltelastomer-fabric interface. It is believed that in addition to itsability to allow the wear-resistant composite through a greater portionof the total fabric thickness than would be possible according to otherprocesses or constructions, the fabric treatment and/or subsequenttreatment or treatments set forth above furthermore provide at least apartial barrier or boundary layer between the wear-resistant compositeand fabric cover element on one hand, and the belt body elastomer on theother. Adhesion between the fabric layer and the underlying beltelastomer may thus be accomplished by more conventional or practicalmeans, e.g., the adhesive compositions here generally described, or anysuitable and/or conventional adhesive system. Moreover, because thewear-resistant composite preferably penetrates to great measure within asignificant portion of the fabric cover, including within fiber bundlesand fabric interstices, it likely resists shearing off even under highmechanical stress.

In a more preferred embodiment of the present invention, a fabric isselected for use as the fabric cover element, which possesses a weave, awarp and weft yarn type and yarn quantity, which combine to define aspecific porosity characterized in that it prevents significantencroachment of the wear-resistant composite to the side of the fabricfacing and intimately positioned along the underlying belt elastomer.This is distinguishable from those constructions wherein a fabricconstruction is selected to prevent encroachment of the belt body ortooth elastomer to the outer, sprocket- or sheave-engaging surface ofthe belt. In the latter instance, encroachment of the belt elastomerthrough fabric interstices may be reduced or prevented by a relativelyloose weave, or high porosity fabric, in that such elastomeric materialstypically possess a relatively high viscosity, even at relatively hightemperatures. Conversely, in the former instance, the typically very lowviscosity of coating materials render reduction or prevention of theirencroachment through the fabric in the direction of the belt body muchmore difficult. In this preferred embodiment, a preferred fabric isformed of a substantially pure nylon 6,6 and contains yarns having atensile strength of not less than 6.0 g/decitex in their initial statein both the warp and weft directions. One direction is preferably woolly(textured) processed giving the fabric not less than 80% stretch under 2kg load, as measured on a 25 mm strip. The fabric preferably isconstructed to yield a finished weight of at least 385 g/m² of which atleast 90% of the weight is preferably in the woolly processed direction,i.e., in the direction of belt travel. According to this same preferredembodiment of the invention, it is believed that the wear-resistantcomposite is greatly restricted, or essentially prevented, fromcontacting the inner, belt elastomer-contact surface of the fabric coverelement. While at least one of the fabric cover element treatment, thesecond treatment and the adhesive treatments disclosed above, inaddition to allowing the wear-resistant composite through at least aportion the fabric, form a significant barrier or boundary between thefabric layer and the underlying belt elastomer, it is believed that theincorporation of such low porosity fabric would further enhance thisaspect of the invention. Where no such boundary layer exists between thefabric and coating layer on the one hand and the belt body elastomer onthe other, it is believed that delamination and diminished operatingcapacity of the belt would likely occur under extended operation,particularly under high load conditions.

Any suitable and/or conventional method may be employed in performingthe balance of the steps required to build the power transmission beltsof the present invention. For example, where castable belt elements areutilized in toothed belt manufacture, the production steps mayfurthermore include wrapping the composite-bearing wear-resistant fabricabout the surface of a notched mold portion in a manner such that thecomposite-coated surface of the fabric cover element is adjacent thenotched mold portion; applying a tensile layer about the wear-resistantfabric, such as by helically winding one or more tensile cords about thefabric; introducing a substantially liquid elastomeric material into themold cavity; and polymerizing the thus formed product. Wherenon-castable belt elastomers are utilized, i.e., millable gum rubbers,either with or without fiber loading, the remaining belt building stepsmay include those of positioning the composite-coated fabric coverelement as described above within an appropriately configured moldcavity having notch portions for the formation of teeth; disposing atensile member against the second surface of the fabric cover element,such as by helically winding one or more tensile cords about the fabric;disposing elastomeric material against the tensile member; disposingadditional alternating arrangements of tensile members and/orelastomeric material against this tensile member as required of a givenconstruction; applying sufficient temperature and pressure to cure orvulcanize the elastomer materials; and removing the assembly from themold cavity. The tooth portions of such belts may moreover have anysuitable shape, including curvilinear, trapezoidal, etc.

In a preferred embodiment of the present invention, the wear-resistantcomposite and various fabric—and adhesive treatments are performed andthe thus-treated fabric cover element applied to the belt, prior tovulcanization or curing of the elastomeric belt elements. Thereafter,the assembly may be vulcanized or cured as appropriate for thecomponents.

Wear and the dimensional changes accompanying wear are primary sourcesof belt slip noise, impact noise and premature failure in endlesstoothed belts. In order to compare the dimensional stability and wearcharacteristics of a belt made in accordance with the provisions of thepresent invention to other, less desirable constructions, some of whichmay be found in the prior art, several belts were constructed asdescribed below in Table 1, and were subjected to a room temperaturewear-resistance analysis. The test apparatus consisted of a two-pulleydrive arrangement, with each pulley having 19 grooves and a RU profile.The belts were operated at a speed of 6300 RPM as measured on thepulley, at a tension between the pulleys of 530 N, with a belt pitch of0.375 inches (9.52 5 mm). The test was conducted at 25°±5° C. TABLE 1Belt Constructions for Wear-Resistance Analysis Belt 1 Comparative BeltA Comparative Belt B Comparative Belt C Overcord and HNBR HNBR HNBR HNBRtooth elastomer fabric cover Yes Yes Yes Yes cover treatment Fabricimmersed Fabric immersed Fabric immersed Fabric immersed into treatmentinto treatment into treatment into treatment material. material.material. material. Treatment pick- Treatment pick- Treatment pick-Treatment pick- up of 10-20% up of 30-40% up of 30-40% up of 30-40%wear-resistant Applied to pulley Applied to pulley Applied to fabricNone composite side of treated side of treated on pre-vulcanized fabric;fabric fabric; fabric belt. thereafter applied thereafter applied tobelt, and belt to belt, and belt vulcanized. vulcanized.

In the above example and comparative examples, except as provided inTable 1, belts were generally constructed according to the descriptionprovided above for FIG. 1. The belts were each constructed to be 15 mmwide and to have 97 longitudinally spaced teeth of equivalentdimensions, with a 9.525-mm pitch. The belt overcord section and toothportions in each case comprised an HNBR elastomer composition containingapproximately 60 parts per hundred weight of elastomer (phr) of Carbonblack, about 15 phr of plasticizer, about 3.5 phr of zinc oxide, about 2phr of sulfur, and a dithiocarbamate curative. The fabric cover in eachcase comprised nylon 6.6 yarns in a 2×2-twill weave, wherein the weftyarn was false twist texturized. The fabric cover treatment material inall instances comprised a resorcinol-formaldehyde latex/elastomer blendcompatible with the HNBR belt body elastomer. The wear-resistantcomposite consisted in each case of a fluorocarbon coating comprising50:50 by weight mixture composition available by Whitford Plastics Ltd.,under the trademark, XYLAN (blend of XYLAN 1642-A-1429 and 1642-B-1452).Each belt further comprised a resin-based, rubber-bonding adhesivecement produced by Compound Ingredients Ltd., under the trademark,CILBOND 80, at a pick-up of about 16% based on the dry fabric weight andan additional adhesive comprising a HNBR composition dissolved in methylethyl ketone at a concentration of approximately 28%, at a pick up rateof about 55% based on the dry fabric weight.

For the comparison, the belts were first weighed, then mounted on thetest apparatus and then re-weighed after 150 hours on test to compareweight loss among the various constructions. Belt 1 experienced a weightloss of 0.26 grams; Comparative Belt A experienced a weight loss of 0.45grams; Comparative Belt B experienced a weight loss of 0.6 grams; andComparative Belt C experienced a weight loss of approximately 1.6 grams.While each of the comparative examples employing the wear-resistantcomposite layer or coating theoretically possessed the same effectivecoefficient of friction as that of Belt 1 of the present invention, thelatter exhibited greatly improved wear resistance over each of thecomparative examples. The results of this analysis indicate that theinventive belts incorporating the wear resistant composite as theirpower transmitting surface interface portions exhibit substantiallyimproved dimensional stability and wear resistant characteristicscompared to belts having no wear-resistant composite coating, as well ascompared to those belts employing a similar composite applied in adifferent manner or according to a different process. The belts of thepresent invention are thus likely to enjoy substantially longeroperating life under high load and/or high-speed conditions, as well asdecreased slip and impact noise. It is presently believed that the beltsof the present invention would be able to tolerate significantly highertension in use compared to known belt constructions, due to theinventive belts' improved abrasion- or wear-resistance performancecapabilities, as well as their excellent mechanical characteristics.

Although the present invention has been described in detail for thepurpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by oneskilled in the art without departing from the spirit or scope of thepresent invention except as it may be limited by the claims. Theinvention disclosed herein may suitably be practiced in the absence ofany element which is not specifically disclosed herein.

1-16. (canceled)
 17. A method for the manufacture of a powertransmission belt (10) having a fabric cover (22) element positionedintimately along at least a portion of the outer surface of anelastomeric belt body, said fabric cover element (22) having a generallyalternating arrangement of yarns and voids, the method characterized inthat: a) said fabric cover element (22) is treated with a fabrictreatment material comprising at least one cross-linkable constituent,such that at least a portion of said voids remain at least partiallyfree of said fabric treatment material; b) a wear-resistant composite(20) comprising at least one binder constituent and at least onefriction-modifying constituent is applied to a first surface only ofsaid fabric cover element forming a power transmitting surface of thebelt (10); c) at least a portion of said wear-resistant composite (20)is caused to penetrate into at least a portion of the total thickness ofsaid fabric cover element but does not penetrate through the entirethickness thereof, such that at least a portion of saidfriction-modifying constituent resides within one or more said voids insaid fabric cover element (22); and d) at least a portion of saidwear-resistant composite (20) is polymerized.
 18. The method of claim 17further characterized in that said fabric cover element (22) is appliedto said surface of said elastomeric belt body after application of saidwear-resistant composite (20) to said fabric cover element.
 19. Themethod of claim 17 further characterized in that at least a portion ofsaid friction-modifying constituent is separated from at least a portionof said binder constituent by a boundary.
 20. The method of claim 17further characterized in that said fabric treatment material is appliedsuch that a pick-up rate of from about 1% to less than about 50% byweight of the dry fabric is achieved.
 21. The method of claim 17 furthercharacterized in that said fabric treatment material is applied suchthat a pick-up rate of from about 1% to about 30% by weight of the dryfabric is achieved.
 22. The method of claim 17 further characterized inthat a second treatment material comprising at least one cross-linkableconstituent is applied to a second surface of said fabric cover element(22) after application of said wear-resistant composite (20), saidsecond surface being opposite that surface on which said wear-resistantcomposite is applied.
 23. The method of claim 22 wherein the pick-uprate of said second treatment material within said fabric cover elementis from about 2.5% to about 55% based on the dry fabric weight.
 24. Themethod of claim 17 further characterized in that at least one rubberbonding adhesive composition is applied to a second surface of saidfabric cover element (22), said second surface being opposite to thesurface on which said wear-resistant composite (20) is applied, and eachsaid rubber bonding adhesive composition is applied at a pick-up rate insaid fabric cover element (22) of up to about 70% based on the dryfabric weight.
 25. The method of claim 22 further characterized in that,following application of said second treatment material, at least onerubber bonding adhesive composition is applied to at least said secondsurface of said fabric cover element (22), and each said rubber bondingadhesive composition is applied at a pick-up rate in said fabric coverelement of up to about 70% based on the dry fabric weight.
 26. Themethod of claim 17 further characterized in that it comprises applyingsaid fabric cover element (22) to said portion of the outer surface ofthe elastomeric belt body, followed by vulcanizing the elastomeric beltbody.
 27. A method according to claim 17 for the manufacture of atoothed power transmission belt wherein the elastomeric body portion ofsaid belt is tensile-loaded, and a plurality of spaced teeth (16) arebonded with and disposed along at least the inner periphery of the bodyportion, wherein: a) said fabric cover element (22) is immersed saidfabric treatment material to effect a pick-up rate of from about 1% toless than about 50%, based on the dry fabric weight; b) thewear-resistant composite is applied to the first surface of said fabriccover element forming the power transmitting surface of said belt; c)the fabric cover element is applied to the outer surface of said beltbody; and d) the belt body is vulcanized.
 28. The method of claim 27further characterized in that a second treatment material comprising atleast one cross-linkable constituent is applied to a second surface ofsaid fabric cover element prior to said application of said fabric coverelement (22) to said belt body surface, said second surface beingopposite that surface on which said wear resistant composite is applied.29. The method of claim 28 further comprising the step of applying atleast one additional rubber bonding adhesive composition to said secondsurface prior to said vulcanization
 30. A method for the manufacture ofa power transmission belt (10) having a fabric cover (22) elementpositioned intimately along at least a portion of the outer surface ofan elastomeric belt body, said fabric cover element (22) having agenerally alternating arrangement of yarns and voids, the methodcharacterized in that: a) said fabric cover element (22) is treated witha fabric treatment material comprising at least one cross-linkableconstituent, such that at least a portion of said voids remain at leastpartially free of said fabric treatment material, said fabric treatmentmaterial being applied such that a pick-up rate of from about 1% toabout 50% by weight of the dry fabric is achieved; b) a wear-resistantcomposite (20) comprising at least one binder constituent and at leastone friction-modifying constituent is applied to at least a firstsurface of said fabric cover element forming a power transmittingsurface of the belt (10); c) at least a portion of said wear-resistantcomposite (20) is caused to penetrate into at least a portion of thetotal thickness of said fabric cover element but does not penetratethrough the entire thickness thereof, such that at least a portion ofsaid friction-modifying constituent resides within one or more saidvoids in said fabric cover element (22); and d) at least a portion ofsaid wear-resistant composite (20) is polymerized.
 31. The method ofclaim 30 further characterized in that a second treatment materialcomprising at least one cross-linkable constituent is applied to asecond surface of said fabric cover element (22) after application ofsaid wear-resistant composite (20), said second surface being oppositethat surface on which said wear-resistant composite is applied.
 32. Themethod of claim 30 wherein the pick-up rate of said second treatmentmaterial within said fabric cover element is from about 2.5% to about55% based on the dry fabric weight.
 33. The method of claim 30 furthercharacterized in that at least one rubber bonding adhesive compositionis applied to a second surface of said fabric cover element (22), saidsecond surface being opposite to the surface on which saidwear-resistant composite (20) is applied, and each said rubber bondingadhesive composition is applied at a pick-up rate in said fabric coverelement (22) of up to about 70% based on the dry fabric weight.
 34. Themethod of claim 31 further characterized in that, following applicationof said second treatment material, at least one rubber bonding adhesivecomposition is applied to at least said second surface of said fabriccover element (22), and each said rubber bonding adhesive composition isapplied at a pick-up rate in said fabric cover element of up to about70% based on the dry fabric weight.
 35. A method according to claim 30for the manufacture of a toothed power transmission belt wherein theelastomeric body portion of said belt is tensile-loaded, and a pluralityof spaced teeth (16) are bonded with and disposed along at least theinner periphery of the body portion, wherein: a) said fabric coverelement (22) is immersed said fabric treatment material to effect apick-up rate of from about 1% to less than about 30%, based on the dryfabric weight; b) the wear-resistant composite is applied to the firstsurface of said fabric cover element forming the power transmittingsurface of said belt; c) the fabric cover element is applied to theouter surface of said belt body; and d) the belt body is vulcanized. 36.The method of claim 35 further characterized in that a second treatmentmaterial comprising at least one cross-linkable constituent is appliedto a second surface of said fabric cover element prior to saidapplication of said fabric cover element (22) to said belt body surface,said second surface being opposite that surface on which said wearresistant composite is applied.
 37. The method of claim 36 furthercomprising the step of applying at least one additional rubber bondingadhesive composition to said second surface prior to said vulcanization.38. A power transmission belt (10) comprising a fabric cover element(22) positioned intimately along at least a portion of the outer surfaceof an elastomeric belt body, said fabric cover element (22) having agenerally alternating arrangement of yarns and voids; a wear-resistantcomposite (20) comprising at least one binder constituent and at leastone friction-modifying constituent bonded to a first surface only ofsaid fabric cover element (22) forming a power transmitting surface ofthe belt; and characterized in that: at least a portion of saidwear-resistant composite penetrates into at least a portion of the totalthickness of said fabric cover element but does not penetrate throughthe entire thickness thereof, such that at least a portion of saidfriction-modifying constituent resides within one or more said voids insaid fabric cover element, and is separated from at least a portion ofsaid binder constituent by a boundary; and at least a portion of saidwear-resistant composite is polymerized, and at least a portion of saidwear-resistant composite is separated from said belt body portion by abarrier.
 39. A power transmission belt (10) according to claim 38, whichis obtainable by the method of claim
 17. 40. The power transmission belt(10) of claim 38 wherein said barrier comprises at least one of saidfabric treatment material and a second treatment material containing atleast one cross-linkable constituent.
 41. The power transmission belt(10) of claim 38 wherein said barrier comprises said fabric coverelement, said fabric cover element possessing a weave, a warp and weftyarn type and a warp and weft yarn quantity, which together with saidvoids define a porosity, said porosity being characterized in that saidwear-resistant composite penetrates less than the entire thickness ofsaid fabric cover element.